ldd prints the shared objects (shared libraries) required by each
program or shared object specified on the command line. An example
of its use and output is the following:
$ ldd /bin/ls
linux-vdso.so.1 (0x00007ffcc3563000)
libselinux.so.1 => /lib64/libselinux.so.1 (0x00007f87e5459000)
libcap.so.2 => /lib64/libcap.so.2 (0x00007f87e5254000)
libc.so.6 => /lib64/libc.so.6 (0x00007f87e4e92000)
libpcre.so.1 => /lib64/libpcre.so.1 (0x00007f87e4c22000)
libdl.so.2 => /lib64/libdl.so.2 (0x00007f87e4a1e000)
/lib64/ld-linux-x86-64.so.2 (0x00005574bf12e000)
libattr.so.1 => /lib64/libattr.so.1 (0x00007f87e4817000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f87e45fa000)
In the usual case, ldd invokes the standard dynamic linker (see
ld.so(8)) with the LD_TRACE_LOADED_OBJECTS environment variable set
to 1. This causes the dynamic linker to inspect the program's
dynamic dependencies, and find (according to the rules described in
ld.so(8)) and load the objects that satisfy those dependencies. For
each dependency, ldd displays the location of the matching object and
the (hexadecimal) address at which it is loaded. (The linux-vdso and
ld-linux shared dependencies are special; see vdso(7) and ld.so(8).)
Security
Be aware that in some circumstances (e.g., where the program speci‐
fies an ELF interpreter other than ld-linux.so), some versions of ldd
may attempt to obtain the dependency information by attempting to
directly execute the program, which may lead to the execution of
whatever code is defined in the program's ELF interpreter, and per‐
haps to execution of the program itself. (In glibc versions before
2.27, the upstream ldd implementation did this for example, although
most distributions provided a modified version that did not.)
Thus, you should never employ ldd on an untrusted executable, since
this may result in the execution of arbitrary code. A safer alterna‐
tive when dealing with untrusted executables is:
$ objdump -p /path/to/program | grep NEEDED
Note, however, that this alternative shows only the direct dependen‐
cies of the executable, while ldd shows the entire dependency tree of
the executable.

ldd does not work on a.out shared libraries.
ldd does not work with some extremely old a.out programs which were
built before ldd support was added to the compiler releases. If you
use ldd on one of these programs, the program will attempt to run
with argc = 0 and the results will be unpredictable.

This page is part of release 4.16 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
2017-09-15 LDD(1)